The present invention relates to a motor speed control circuit and, more particularly, to a control circuit for controlling a motor speed in response to a pulse signal having a pulsewidth indicating a desired rotation speed.
A control system has been developed wherein a pulse signal is applied to a motor to control the rotation speed in accordance with a pulsewidth of the applied pulse signal. More specifically, a pulse controlled motor is developed, wherein the pulsewidth of the drive signal is lengthened when the rotation speed of the motor is slower than a desired value. In such a system, a large amount of energy is suddenly applied to the motor because the pulse shaped drive signal is applied directly to the motor. This drive method shortens an operation life of the motor because the intermittent drive deteriorates brushes and commutators included in the motor. Further, noises are inevitably developed and the bearing system must tolerate the rapid change of the rotation speed.
However, the pulsewidth control system is very effective because accurate control is achieved by a simple control circuit.
Accordingly, an object of the present invention is to provide a motor speed control circuit for ensuring a accurate control and a long motor life.
Another object of the present invention is to stabilize the pulsewidth control operation in a motor speed control system.
Still another object of the present invention is to provide a novel motor speed control system which enjoys the feature of the pulsewidth control system and minimizes the disadvantages held by the conventional pulsewidth motor speed control system.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objects, pursuant to an embodiment of the present invention, a conversion system is provided for converting a pulsewidth drive signal into a voltage signal indicative of a difference between the actual rotation speed and a desired rotation speed represented by the pulsewidth control signal. In a preferred form, the conversion system includes a charge discharge circuit having a capacitor in which the charge level is varied in response to the difference between the actual rotation speed of the motor and a desired rotation speed indicated by the pulsewidth control signal.